Sendai virus intra-host population dynamics and host immunocompetence influence viral virulence during in vivo passage

Peña, José; Chen-Harris, Haiyin; Allen, Jonathan E.; Hwang, Mona; Elsheikh, Maher; Mabery, Shalini; Bielefeldt-Ohmann, Helle; Zemla, Adam T.; Bowen, Richard A.; Borucki, Monica K.

When changes in consensus occur they often involve discrete regions of the genome such as the HN protein and were usually preceded by increased frequency of the variant across diet groups (Supplementary Table S2 ). Our data show enrichment for three amino acid changes in the HN protein during passage, including residue 461, which is known to affect protein function (Takahashi, Ryan, and Portner 1992; Baumann and Neubert 2010) and virulence (Kiyotani et al. 2001; Fujii et al. 2002) . The presence of Lys at 461 rather than Glu is known to decrease HN neuraminidase activity without affecting binding of the HN protein to the cell receptor. For example, experiments described by Takahashi, Ryan, and Portner (1992) showed that while HN protein of SeV is heat-stable with Lys at 461, it becomes heat-labile when substitutions (Gly or Gln) occur at this position. Position 461 is also associated with virulence in mice, and mutates from a negatively charged residue, Glu, to a nonpolar residue, Gly, in response to passage of an egg-propagated isolate in mouse cells (Kiyotani et al. 2001; Itoh et al. 1992) . Our data show a mutation of Glu, to a positively charged residue, Lys, in response to passage of an egg-propagated isolate in mice. These data indicate that HN 461 is not only a variable residue but also important for host tropism.